The present invention relates to the use of (oxidized) thioethers of polyalkylene oxides in washing and cleaning compositions, especially in dishwashing compositions, and to washing and cleaning compositions, especially dishwashing compositions, which comprise (oxidized) thioethers of alcohol alkoxylates. These (oxidized) thioethers are especially suitable as surfactants with rinse aid function (rinse aid surfactants). “Oxidized” relates to the sulfur atom in the thioether, which may be present in oxidized form as sulfoxide (SO) or sulfonyl (SO2). The invention also relates to particular oxidized thioethers of polyalkylene oxides.
Surfactants are substances which can lower interfacial tension. Typically, surfactants possess a characteristic structure and have at least one hydrophilic and at least one hydrophobic functional group. When the two parts of the molecule are in equilibrium with respect to one another, the substance will accumulate and become aligned at an interface, i.e. hydrophilic groups point, for example, into an aqueous phase and the hydrophobic groups in the direction of other solid, liquid or gaseous phases. A further special feature of surfactants is the formation of higher aggregates, known as micelles. In these, the surfactant molecules become ordered in such a way that the polar groups, for example, form a spherical surface. This has the effect that substances such as soil particles are solubilized in an aqueous solution with formation of micelles. Surfactants are therefore suitable especially for cleaning surfaces and as an additive in washing compositions.
Surfactants which have a hydrophobic block and a hydrophilic block are widespread. However, their tendency to form foam makes them unsuitable or suitable only to a limited degree for many applications. For applications in which strong foam formation is unwanted, therefore, nonionic surfactants which have a second hydrophobic block have been developed, which limits the foam volume.
The second hydrophobic block can derive, for example, from a fatty alcohol. However, the use of dishwashing compositions which comprise such a surfactant, especially of dishwashing compositions for machine dishwashers, frequently leads to residues remaining on the dishware cleaned therewith (deposit formation; called “spotting” in the case of formation of spot deposits or “filming” in the case of film-like deposits).
The second hydrophobic block can alternatively derive from a fatty acid. In the case of dishwashing compositions which comprise such surfactants, the problem of deposit formation is no longer as great; however, these surfactants are hydrolysis-sensitive due to the ester group, which greatly restricts the usability thereof in alkaline formulations and at relatively high temperatures, especially in prolonged washing operations.
Thioethers of polyalkylene oxides are known, for example from U.S. Pat. No. 5,593,953, where the use thereof as lubricant additives is described, or from WO 93/02387, where they are used in photographic high-contrast elements for prevention of pepper fog. Use as a washing or cleaning composition is not mentioned.